Long-Lasting Weed Control In Almonds

Almond Orchard Herbicide Trial

Nut harvest is over and, barring another dry winter, the fall rains should be starting up in the Western tree nut production regions. Now is the time when nut producers and their pest control advisors should be developing or fine tuning weed management programs for the upcoming growing season.

Over the past decade, many tree nut growers shifted to weed control programs based on postemergence (POST) herbicides such as glyphosate. Although this strategy has been fairly cost effective in the short term, the need for multiple post treatments, shifting weed populations, new herbicide registrations, and the evolution of glyphosate-resistant weeds have increased interest in residual herbicide programs in recent years.

Why Consider A Residual Herbicide Program?

Residual herbicides (also known as preemergence [PRE], or soil-applied herbicides) are usually applied in the orchard before weeds are present; the material persists in the soil at high enough concentrations for some period of time to control weeds that germinate after the treatment. Conversely, herbicides with primarily POST activity control only weeds that are present at the time of application and do not affect subsequent flushes of germinating weeds. A few important orchard herbicides have both PRE and POST activity.

Residual herbicides, typically applied in the late fall or early winter and incorporated into the soil by winter rains, can provide an important start for a season-long orchard weed management program. With appropriate product selection, application rates, and tank-mix partners, residual herbicides often can extend control of winter and summer annual weeds well into the growing season.

There are several benefits to a chemical weed management program that includes both PRE and POST herbicides either in a tank mix or sequential application during the year. Most herbicides with PRE activity are taken up by the roots or shoots of very small weed seedlings shortly after germination, and affected weeds usually fail to emerge or die shortly after emergence. Because any weeds controlled at the seedling stage by the residual herbicide do not have to be controlled later by POST applications, residual herbicides can sometimes reduce the number of POST applications needed. Additionally, the efficacy of later POST applications is often improved following PRE applications because of better spray coverage in less dense weed canopy. This is especially important for POST herbicides that are not translocated (i.e. “contact” herbicides). PRE herbicides applied during the late fall or early winter when orchard access is more certain also can help keep tree rows clear of weeds during periods where timely POST applications are delayed due to weather or soil conditions later in the winter.

Reducing the number of POST applications applied to the tree rows may increase crop safety due to fewer opportunities for non-selective POST herbicides to come in contact with green bark or foliage due to direct application or drift. With the exception of grass-specific herbicides, POST products registered in orchards have little inherent crop safety; instead, safety depends on placement to minimize tree exposure. Because crop safety is dependent on placement, low hanging branches, rootstock suckers, trunks with green or thin bark, and herbicide drift all can lead to tree injury from POST herbicides.

The recent increase in herbicide resistant weeds is one of the most important reasons to consider a residual herbicide program. The primary recommendation for managing herbicide-resistant weeds is to include multiple herbicide modes of action (MOA) in rotation or in sequence. Because many of the currently available residual herbicides have different MOA than commonly used POST products, residual herbicides can help manage existing herbicide-resistant populations and reduce selection pressure for addition resistant species. However, there are no PRE products with the same MOA as glyphosate; thus, including an appropriate residual herbicide can help to reduce the impact of glyphosate-resistant weeds in tree nut orchards. A listing of common orchard herbicides and mode of action information
can be found at http://wric.ucdavis.edu/PDFs/herbicide_registration_on_horticultural_tree_and_vine_%20crops_2012_01.pdf.

Current Residual Herbicide Research

As part of our ongoing research in orchard and vineyard crops, we conduct field trials each year to evaluate residual herbicides alone and in various tank-mix combinations. Several materials have provided good to exceptional weed control for two to six months after treatment, depending on the weed spectrum present. Recent trials have focused on late applications of tank mixes of residual and POST herbicides to control existing weeds while extending residual control further into the season. This work has highlighted the importance of selecting the right tank-mix partners.

While a complete rundown of our research results is not possible here, this information is routinely presented to California nut growers and pest control advisers at University of California (UC) Cooperative Extension meetings and field days across the state, at industry-sponsored events, at the California Weed Science Society annual meeting, and at the annual UC Weed Day. Many of these results are also available online at the UC Weed Science blog (http://ucanr.org/blogs/UCDWeedScience), the UC Weed Research and Information Center (http://wric.ucdavis.edu) or at my UC lab web page (www.plantsciences.ucdavis.edu/plantsciences_faculty/hanson/main/Recent%20Outreach.html).

 For 9 Tips On Improving Herbicide Efficacy, go to the next page

Topics:

Leave a Reply

Nuts Stories
Photo credit: USDA
Citrus
May 23, 2016
World Health Organization Experts: Glyphosate Not Carcinogenic
Risk unlikely when consuming crops treated with herbicide. Read More
nutcracker crunching down on a walnut
Nuts
May 20, 2016
Bank Predicts A Roller Coaster Ride For Tree Nut Industry
Supply expected to grow by more than one-third in next five years, but decreasing demand may lower prices. Read More
close-up of a merge ahead traffic sign
Citrus
May 19, 2016
Bayer Makes Bid For Monsanto
Monsanto says proposal is being reviewed by board of directors as well as legal and financial advisors. Read More
(Photo credit: USDA)
Citrus
May 17, 2016
$130 Million In Funds For Fruit And Vegetable Education And Research
USDA allocates funds for Extension, organic production, food safety, and technology grants. Read More
A two-spotted spider mite. (Photo credit: www.bugwood.org)
Insect Control
May 16, 2016
Tips For Balancing Almond Mites And Predators
Almond growers need to do a delicate dance to keep spider mite populations down, but not so far that beneficial Read More
Almonds
Nuts
May 14, 2016
Almond Hullers And Processors Association Rebrands, Retools
The Almond Hullers and Processors Association (AHPA) renamed itself the Almond Alliance of California at its annual convention in April, Read More
handshake feature image
Fertilizer
May 13, 2016
Northeast Ag Sales To Distribute Agro-K Fertilizer Products
Partnership to all New England states enhanced access to full line of foliar plant nutrition and soil biological items. Read More
The Latest
Insect Control
May 26, 2016
Temperature, Location Key To Predicting …
This year, leaffooted bugs are expected to be a significant problem in almonds and pistachios, but watching temperature and the Read More
Fruits
May 26, 2016
Consider Fumigating For Nematodes Before…
Stone fruit and almond growers looking to replant orchards might want to invest in soil samples to assess nematode populations Read More
Citrus
May 25, 2016
Monsanto Says Bayer Bid ‘Financially Ina…
Proposal cited as undervalued, not able to address financial, regulatory risks. Read More
Citrus
May 23, 2016
World Health Organization Experts: Glyph…
Risk unlikely when consuming crops treated with herbicide. Read More
Nuts
May 20, 2016
Bank Predicts A Roller Coaster Ride For …
Supply expected to grow by more than one-third in next five years, but decreasing demand may lower prices. Read More
Citrus
May 19, 2016
Bayer Makes Bid For Monsanto
Monsanto says proposal is being reviewed by board of directors as well as legal and financial advisors. Read More
Citrus
May 17, 2016
$130 Million In Funds For Fruit And Vege…
USDA allocates funds for Extension, organic production, food safety, and technology grants. Read More
Insect Control
May 16, 2016
Tips For Balancing Almond Mites And Pred…
Almond growers need to do a delicate dance to keep spider mite populations down, but not so far that beneficial Read More
Nuts
May 14, 2016
Almond Hullers And Processors Associatio…
The Almond Hullers and Processors Association (AHPA) renamed itself the Almond Alliance of California at its annual convention in April, Read More
Fertilizer
May 13, 2016
Northeast Ag Sales To Distribute Agro-K …
Partnership to all New England states enhanced access to full line of foliar plant nutrition and soil biological items. Read More
Fruits
May 10, 2016
California Governor Signs Executive Orde…
Rule updates existing requirements for agriculture water management plans. Read More
Citrus
May 10, 2016
Survey: Beekeepers Lost 44% Of Bees Last…
Responses indicate summer losses rival winter losses for second year in a row. Read More
Citrus
May 4, 2016
$6 Million Available For Antimicrobial R…
Program to develop strategies to reduce public health risks in food chain. Read More
Nuts
May 2, 2016
California Almond Acreage Up 6%
The increase follows a trend in which acreage has doubled in the last 20 years. Read More
Nuts
April 29, 2016
Look Out For Jacket Rot On Almond Leaves
Rains at bloom are causing higher than normal incidents of bacterial infections. Read More
Citrus
April 26, 2016
Farm Bureau Says Labor Visa Backlogs Thr…
Agency calls for swifter processing of paperwork so growers' requests for crews can be met. Read More
Equipment
April 22, 2016
Whole Orchard Recycling Could Improve So…
A giant new machine gobbles up whole trees and spits out the chunks, which eventually get worked back into the soil. Read More
Nuts
April 20, 2016
California Legislators Give Preliminary …
California experienced 158 cargo theft incidents in 2015, costing businesses nearly $19 million – more than any other state. Read More
[gravityform id="62" title="false" description="false"]